1. Field of the Invention
The invention relates to a device for detecting thermal radiation of the type having at least one thermal detector element to convert the thermal radiation into an electrical signal, and to a method of production of such a device.
2. Description of the Prior Art
A device for detecting thermal radiation is known from, for example, DE 100 04 216 A 1. This device is described as a pyro-detector. The detector element is a pyro-electrical detector element. It has a layer construction comprising two electrode layers with a pyro-electrical layer having pyro-electrical sensitive material arranged between the electrode layers. This material is Lead Zirconate Titanate (PZT). The electrodes comprise, for example, platinum or of a heat-absorbing chromium/nickel alloy.
The thermal detector element is connected to a detector support made of silicon (silicon-wafer). To provide electrical and thermal insulation between the detector element and the detector support an insulating layer is arranged between the detector element and the detector support. The insulating layer has an evacuated cavity which extends over an area of the detector element, a support layer for the cavity and a cover over the support layer and the cavity. The support layer comprises poly-silicon. The cover is made of a boron-phosphorus-Silicate glass (BPSG). To read out, process and/or further transmit the electrical signals produced by the detector element a readout circuit is integrated in the detector support. The readout circuit is produced by the application of CMOS (Complementary Metal Oxide Semiconductors) technology.
A comparable device for detecting thermal radiation is known from DE 195 25 071 A1. The thermal detector element is also a pyro-electrical detector element as described above. The detector element is arranged on a multilayer detector support. The detector element is applied to a silicon layer of the detector support at one of its electrode layers. The silicon layer is located on an electrically insulating membrane of the detector support. The membrane is formed, for example, as a triple layer—namely Si3N4/SiO2/Si3N4. Once again, the membrane is applied to a silicon substrate of the detector substrate. The silicon substrate has a radiation window (detection window) with an area which for all practical purposes corresponds with an area of the pyro-electrical detector element. The radiation window is an aperture in the silicon substrate. Thereby, the support material (silicon) of the substrate is removed down to the membrane. The thermal radiation passes through the radiation window to the detector element where it produces an electrical signal which can be evaluated. In that respect the membrane distinguishes itself by providing a suitable means of transmission of the thermal radiation. In the silicon layer displaced laterally relative to the detector element a readout circuit for the electrical signal is integrated. The detector support also functions as a circuit support for the readout circuit.
In the case of the known detectors, a number of detector elements may be provided (detector element array). In that situation the electrical signal from each of the detector elements is to be read out separately. Normally, electrical contact with the electrode layers of each of the detector elements is effected by bonding wires. However, this means that considerable space is required for the wiring of the detector elements which results in a limited, relatively low packing density of the detector elements (number of detector elements per unit area of the detector support).